Zagreb - Croatia begins enforcing a ban on smoking in most indoor areas Wednesday, threatening the estimated one-quarter of its population which lights up with stiff fines.

Smokers caught in cafes, restaurants and bars face a fine of 1,000 kuna (180 dollars), while operators tolerating obstinate smokers may have to pay up to 15,000.

The comprehensive ban sets in as a six-month transition period since the law on smoking was passed expires. Some areas, such as schools and hospitals, were declared smoke-free already last year.

There is an exemption from the rule - Croatian law allows smoking in psychiatric hospitals. Doctors explained that mentally ill smokers could become agitated without their nicotine fill.

Croatian caterers worry the ban would hurt their business and point to Slovenia, where restaurant and bar owners reportedly recorded a 30-50 per cent decline since ostracizing smokers.

An estimated 25-30 per cent of Croatia's 4.5 million people smoke. (dpa)